Every B2B salesperson sweats a ‘meet me in the channel’ meeting with the customer, and a 3rd party ecosystem partner. It happened to me. We went into a customer meeting forced to bring a particular ecosystem partner. There is substantial uncertainty and the associated opportunity risk in engaging a 3rd party ecosystem partner and the customer simultaneously. For the B2B salesperson this is a dreadful situation. In a few months our fears came true, and we had to scramble to save the opportunity.
Ecosystem managers and product managers try their best to avert issues, and bring true value of 3rd party ecosystem partners to the solution. The intent of the ecosystem partnerships is clear, necessary, and adds significant value to the solution. Establishing partnership requires trust, need, value, deep collaboration, and mutual strategic intent. Trust and need are delicate attributes, and they change when people, market, or situation changes. Additionally, while the company invests a lot of cash and resources to engage ecosystem partners with a clear need and strategic intent, most of these programs become dormant and often neglected.
In engaging 3rd party ecosystem partners, B2B salespersons need to focus on 3 key things before setting up a simultaneous 3-way meeting with the customer.

Open collaboration: This is obvious and critical. B2B salespersons must engage the 3rd party ecosystem partner and setup pre-engagement calls. Your customer is very likely to probe, poke, and puncture the strength of the partnership, and test the value proposition during the meeting. It is best to ask and answer the hard questions in a few pre-engagement calls. Independent of the ecosystem partner managers, B2B salespersons must test the partnership strength. Make calls to various people involved in the partnership and ask hard questions. Watch out for responsiveness, and if someone is trying to be circumspect or discreet with their answers.

Establish clear value: Often partnerships that develop out of good intent have clear and established value. However, a marketer establishing value to a segment or a solution is substantially different from identifying the value proposition against a specific need of the customer. B2B salespersons must explore how well the solution from the 3rd party ecosystem partner meets the needs of the customer. Ensure that the expanded team has a clear definition of which customer needs are being met or exceeded.

Remove competitive conflicts: This is a big road-block and potential opportunity killer. Often, 3rd party ecosystem partners establish partnerships with competing companies. If the specific 3rd party ecosystem partner has close relationship with a competitor in the opportunity, completely avoid the partner. You will have to find another way to fill the value gap, potentially with another 3rd party ecosystem partner, or with appropriate price reduction.